Search for: All records

Parabens and salicylates were examined as disinfection byproduct (DBP) precursors to explore the possible influence of ipso substitution (i.e., halogen exchange) on the yield and speciation of trihalomethanes (THMs) formed during water chlorination. Substoichiometric conversion of C–Br bonds into C–Cl bonds was confirmed for several parabens and salicylates. The co-occurrence of (mono)brominated and nonhalogenated precursors in the presence of free chlorine (but in the absence of added Br–) generated polybrominated THMs, implicating ipso substitution. The THM molar yield, bromine incorporation, and bromine recovery from brominated and nonhalogenated precursor mixtures were commensurate with those observed from equimolar additions of NaBr, indicating efficient displacement of aromatic bromine by free chlorine followed by reincorporation of liberated HOBr into DBP precursors. The THM molar yield from brominated precursors was enhanced by a factor of ≤20 relative to that from nonhalogenated precursors. Trends in THM molar yields and bromine incorporation differed between brominated parabens and brominated salicylates, suggesting that the influence of ipso substitution on THM formation varies with the structure of the organic precursor. Collectively, these results provide new evidence of the often-overlooked role ipso substitution can play in promoting halogen exchange and bromine enrichment among DBPs in chlorinated waters. 

Mutation or loss of 6 extracellular matrix collagen genes disrupts annular furrows in adult C. elegans cuticles, causes a wide “Dumpy” body morphology, and activates osmotic, detoxification, and antimicrobial defense genes. High environmental osmolarity reduces internal turgor pressure, physically distorts the epidermis, and activates the same stress responses. Collagen gene mutations that cause Dumpy without furrow disruption do not activate stress responses. These results are consistent with an extracellular damage sensor associated with furrows in the adult cuticle that regulates environmental stress responses in adjacent cells. Several cuticle characteristics change between molts, but all stages have annular furrows and express furrow collagen genes. We compared body shape, furrow organization imaged with differential interference contrast microscopy, and stress response gene expression in furrow collagen gene mutants at all postembryonic stages. We find that most body shape and furrow disorganization phenotypes start at the L3 stage and increase in severity with each molt afterwards. Stress response genes were induced the strongest in adults, correlating with the greatest Dumpy and furrow phenotypes. Although weaker than in adults, osmolyte transporter gene hmit-1.1 and antimicrobial gene nlp-29 were also induced in some early larvae that had weak or undetectable cuticle phenotypes. Our data are consistent with progressive cuticle phenotypes in which each new cuticle is at least partially directed by organization of the former cuticle. Gene expression and cuticle data support the role of furrow disruption as a signal in L4 larvae and adults, but also suggest a role for other cuticle organization or epidermal cell effects in early larvae.

 

We and others previously identified circumferential bands of collagen named annular furrows as key components of a damage sensor in the cuticle of Caenorhabditis elegans that regulates cytoprotective genes. Mutation or loss of noncollagen secreted proteins OSM-7, OSM-8, and OSM-11 activate the same cytoprotective responses without obvious changes to the cuticle indicating that other extracellular proteins are involved. Here, we used RNAi screening to identify protein kinase DRL-1 as a key modulator of cytoprotective gene expression and stress resistance in furrow and extracellular OSM protein mutants. DRL-1 functions downstream from furrow disruption and is expressed in cells that induce cytoprotective genes. DRL-1 is not required for the expression of cytoprotective genes under basal or oxidative stress conditions consistent with specificity to extracellular signals. DRL-1 was previously shown to regulate longevity via a “Dietary Restriction-Like” state, but it functions downstream from furrow disruption by a distinct mechanism. The kinase domain of DRL-1 is related to mammalian MEKK3, and MEKK3 is recruited to a plasma membrane osmosensor complex by a scaffold protein. In C. elegans, DRL-1 contains an atypical hydrophobic C-terminus with predicted transmembrane domains and is constitutively expressed at or near the plasma membrane where it could function to receive extracellular damage signals for cells that mount cytoprotective responses.

 

Parabens are antimicrobial additives found in a wide array of consumer products. However, the halogenated compounds formed from parabens during wastewater disinfection are a potential environmental concern. In order to identify these transformation products and investigate their mechanism of formation, a synthetic route to ethyl parabens labeled with the stable isotope carbon‐13 at specific positions within the benzene ring was developed. This efficient two‐step procedure starts from commercially available¹³C‐labeled phenols and involves (1) initial acylation of the phenol via a Houben–Hoesch reaction with trichloroacetonitrile followed by (2) a modified haloform reaction of the resulting trichloromethyl ketone to afford the corresponding¹³C‐labeled ethyl parabens in 65%–80% overall yield. The scope of the modified haloform reaction was also investigated, allowing for the synthesis of other parabens derived from primary or secondary alcohols, including¹³C‐ and deuterium‐labeled esters. In addition, 4‐hydroxybenzoic acid can be formed directly from the common trichloromethyl ketone intermediate upon treatment with lithium hydroxide. This protocol complements existing methods for preparing¹³C‐labeled paraben derivatives and offers the specific advantages of exhibiting complete regioselectivity in the Houben–Hoesch reaction (to form thepara‐disubstituted product) and avoiding the need for protecting groups in the modified haloform reaction that forms the paraben esters.

 

The rush to remote learning during the COVD‐19 pandemic has caused instructors to rapidly adapt mechanisms of learning. Here, I describe an online concept mapping activity for membrane transport mechanisms that can be accomplished by students working together remotely and either synchronously or asynchronously.

 

CCR4‐NOT is a versatile eukaryotic protein complex that controls multiple steps in gene expression regulation from synthesis to decay. In yeast, CCR4‐NOT has been implicated in stress response regulation, though this function in other organisms remains unclear. In a genome‐wide RNAi screen, we identified a subunit of the CCR4‐NOT complex,ccf‐1, as a requirement for theC. eleganstranscriptional response to cadmium and acrylamide stress. Using whole‐transcriptome RNA sequencing, we show that the knockdown ofccf‐1attenuates the activation of a broad range of stress‐protective genes in response to cadmium and acrylamide, including those encoding heat shock proteins and xenobiotic detoxification. Consistently, survival assays show that the knockdown ofccf‐1decreasesC. elegansstress resistance and normal lifespan. A yeast 2‐hybrid screen using a CCF‐1 bait identified the homeobox transcription factor PAL‐1 as a physical interactor. Knockdown ofpal‐1inhibits the activation ofccf‐1 dependent stress genes and reducesC. elegansstress resistance. Gene expression analysis reveals that knockdown ofccf‐1andpal‐1attenuates the activation ofelt‐2andelt‐3under stress that encode master transcriptional co‐regulators of stress response in theC. elegans, and that overexpression of ELT‐2 can suppressccf‐1's requirement for gene transcription in a stress‐dependent manner. Our findings reveal a new role for CCR4‐NOT in the environmental stress response and define its role in stress resistance and longevity inC. elegans.